This invention relates to the production of simulated meat products from whole soybeans. More particularly, the invention relates to a method of processing whole soybeans to produce textured soy protein products which are free from off-flavors and odors and have a meat-like firmness, texture and appearance.
Considerable effort has been directed by the food industry in recent years toward the production of simulated meat products from vegetable protein materials, particularly soybeans. It is well known that whole soybeans are an excellent source of nutrition. Whole soybeans contain approximately 40% (dry basis) protein of very good quality, and about 20% fat, with the fat being unsaturated. However, whole soybeans have not been widely accepted as a nutritional source in foods for human consumption in many countries. This lack of acceptance is due in large part to the fact that products made from whole soybeans typically have an objectionable flavor and odor characterized as "grassy" or "beany," and that simulated meat products made heretofore from soybean material lack the textural qualities typically associated with meat products.
A variety of procedures have been developed for producing simulated meat products from soy protein materials such as soybean meal, defatted soybean meal, and soy protein isolates and concentrates. Such prior procedures typically produce simulated meat products by methods which involve either the manufacture of protein fibers or the thermoplastic extrusion of soy protein materials. In the manufacture of simulated meat products by protein fiber production, individual filaments or fibers are formed from the soy material, and the fibers are assembled into bundles to which binding agents, coloring and flavor are added and the fiber bundles are shaped to resemble familiar meat products. Procedures for producing such soy protein fibers are disclosed in U.S. Pat. Nos. 2,682,466 to Boyer; 3,482,998 to Carroll et al; and 3,911,159 to Heusdens. The thermoplastic extrusion method of forming simulated meat products from soy protein materials involves subjecting a mixture of soy protein material and water to heat and pressure in an extruder cooker to form a thermoplastic mass, and extruding the mass through a restricted die orifice into an area of reduced pressure to cause the extruded filament to expand and form a fibrous cellular structure. Extrusion procedures for producing protein meat analogs are disclosed in U.S Pat. Nos. 3,488,770 to Atkinson; and 3,496,858 to Jenkins.
These prior procedures suffer from a number of disadvantages which have restricted their widespread acceptability. For example, the amount of texturization is generally proportional to the protein content of the proteinaceous starting material, making it necessary to use soy concentrates and isolates rather than less expensive soy protein materials. Also, such prior processes generally have employed such complex apparatus and procedures that equipment and operating costs have made the textured protein products economically unattractive. In addition, prior procedures have not been entirely successful in masking or eliminating the undesirable bean-like or grassy flavors and odors which are characteristic of soybean materials. As a result, the simulated meat products produced by such prior procedures are of marginal palatability and require the careful control of flavorants to minimize this problem. A variety of procedures have been proposed for the removal of such off-flavors and odors from soy protein products. For example, U.S. Pat. No. 3,142,571 discloses extracting expanded soy protein products with hot water to leach out the undesirable flavors. U.S. Pat. No. 3,642,490 discloses subjecting an aqueous slurry of soy protein isolate to dynamic instantaneous heating while the slurry is dynamically physically worked under positive pressure and then releasing the pressure to cause flash off volatilization of the components causing off-flavors and odors. The resulting slurry is said to have a bland flavor. These prior procedures, which are directed to the removal of off-flavor and odor components from the soy protein material, are only marginally effective in producing soy protein products which are truly free of the objectionable "beany" and "grassy" flavors and odors.
Such objectionable flavors and odors in products produced from soy protein materials result from peroxide reactions associated with polyunsaturated fatty acids in the soybean and is initiated by lipoxygenase enzymes which have an optimum activity at a pH in the range of about 7.0 to 9.0. These reactions occur almost instantaneously when the cell tissue of soybean cotyledons is disrupted in any way in the presence of even a small amount of moisture, and once these off-flavor components have been formed, they are virtually impossible to remove. Prior attempts to reduce this problem by inactivating the lipoxidase enzymes by heat treatment of soybeans has not been successful in preventing the occurrence of such off-flavors.